Legal protection does not guarantee that a protection forest retains its forest cover. This study analysed land cover change over 2015–2025, projected land cover for 2030 under four scenarios, and estimated carbon stocks and emissions in the Meranti Sungai Merah Protection Forest, South Sumatra, Indonesia, an area assigned mitigation actions under Indonesia's Forestry and Other Land Use (FOLU) Net Sink 2030 policy. Land cover was mapped from 10 m Sentinel-2 imagery with the random forest algorithm (overall accuracy 89.9–91.9%; kappa 0.88–0.91). Land cover for 2030 was simulated with a Cellular Automata–Markov model driven by multilayer perceptron transition potentials under business as usual, concession pressure, encroachment restriction and full restoration scenarios. Departing from conventional simulations, the protection forest was not set as a fixed constraint but was allowed to change according to the observed transition patterns. Hindcast validation against the 2025 map gave a figure of merit of 17.8%. Carbon stocks were estimated with the InVEST carbon model, using forest biomass from 51 field plots modelled with the enhanced vegetation index (RMSE 16.07 t ha-1) and national reference values for the other classes. Over 2015–2025, forest cover fell from 83.2% to 51.5% of the area, releasing about 0.96 million t CO2e (96,002 t CO2e year-1). Every scenario remains a net source over 2025–2030, releasing 0.28 million t CO2e (full restoration) to 0.68 million t CO2e (concession pressure). Strictly securing concessions displaces land demand into the protection forest and raises annual emissions 42.44% above the historical baseline, encroachment restriction without restoration lowers them by only 10.0%, and combined protection and restoration lowers them by 42.40%. Retained forest holds far more carbon per hectare than rehabilitated young forest, making the prevention of deforestation the most efficient form of mitigation in this area.